Plants Need Light, But Don't Let Grow Light Burn Your Indoor Plants

 

Each growth stage of a plant requires a distinct light intensity. Insufficient light can lead to stunted or halted growth, while overly intense illumination can burn the plant, causing a range of health issues. When setting up LED grow lights, it's essential to use a light meter to measure the current light strength. Moreover, issues with excessive light are common in many northern and high-altitude regions.

Sample of Light Meter

Lighting Requirements at Different Stages of Plants

The slightest excessive light intensity is like this, the leaves of cannabis will stretch upward. This is because photosynthesis has reached the maximum, and the energy generated by photosynthesis makes the veins of the cannabis leaves tense.

Sign of Slightest Excessive Light Intensity

A slight light burn looks like this, with the leaf tips starting to turn white. This is because the overly strong photosynthesis begins to deprive the regular cells of moisture. The leaf tips, being furthest from the stem, lack a sufficient water supply, and so they are the first to start drying out and turning yellow.

Light Burn Causing Leaves Yellow

If this situation becomes a bit more severe, the edges of the leaves will start to dry out and turn yellow due to lack of water.

Light Burn Leads to Leaves Yellow

If this continues for an extended period, the cells along the leaf edges will lose their vitality and start to curl.

Light Burn Leads to Leaf Edges to Curl

Excessively strong light increases the plant's water metabolism, leading to an overly dry environment. Alternatively, over-watering the plant can also cause this issue. In either case, the plant's root water transport capacity cannot keep up, resulting in root rot. This ultimately leads to widespread wilting and death of the plant.

Some light burn damage can be difficult to detect in the early stages. The top parts of the plant may start to appear a bit paler, and then gradually turn yellow over the course of a few weeks. This issue is not necessarily caused by excessively high light intensity, but rather by prolonged exposure to strong light or the light being too close. This prolonged intense light exposure damages the chlorophyll in the plant cells, causing the plant to lose its green color.

Light Burn Leads to Plants Losing Color

Mild light burn damage can slowly destroy the leaf structure, so the first signs often appear on the older, lower leaves of the plant. Many growers have difficulty connecting the issues with the lower leaves to light burn, and they naturally assume it's due to nutrient deficiency or dry soil. So they water and fertilize excessively, combined with overly strong light, which ends up killing the plant. This is the most treacherous hurdle that new growers face after their seeds have germinated - 90% of successfully germinated plants are killed this way.

Light burn can exacerbate other common problems like over-fertilization, overly wet soil, root rot, and leaf spot diseases. So it's important to have a light meter on hand to determine if light burn is the root cause, to avoid making the situation worse through misguided remedies.

Once a plant shows signs of light burn, the first step is to adjust the environment and give it a comfortable setting to recover for a week. Then, prune off all the damaged leaves - the affected plant tissues cannot be restored, and will only waste the plant's energy and nutrients.